async function async1() {
  console.log("async1 start");
  // 注意这里 await 后面的内容就相当于一个promise的感觉
  await async2();
  console.log("async1 end");
}

async function async2() {
  console.log("async2");
}

async1();

console.log("aaa");

new Promise(function (resolve) {
  console.log("promise1");
  resolve();
  console.log("promise2");
}).then(function () {
  console.log("promise3");
});
